1. Field of the Invention
The present invention relates to a liquid discharge recording head for generating recording liquid small droplets used for ink jet recording, and a method for manufacturing such a head. More particularly, the invention relates to a method of manufacture for producing an ink flow path configuration, as well as a head using such configuration, being capable of discharging micro liquid droplets stably to provide high image quality, and also, implementing high-speed recording.
Further, the invention relates to an ink jet recording head the ink discharge characteristics of which are improved on the bases of the aforesaid method for manufacturing an ink jet head.
2. Related Background Art
The ink jet recording method (liquid discharge recording method) that performs recording by discharging recording liquid, such as ink, is generally provided with a liquid flow path, a liquid discharge energy generating portion, which is provided for a part of such liquid flow path, and a fine recording liquid discharge port (hereinafter referred to as the “orifice”) that discharges liquid in the aforesaid liquid flow path by means of thermal energy given by the liquid discharge energy generating portion. Conventionally, as the method for manufacturing a liquid discharge recording head of the kind, there have been the following among some others, for example:
A method of manufacture in which after forming a through hole for supplying ink on the element base plate where the heaters that generate thermal energy for use of liquid discharge, and driver circuit and others for driving these heaters are formed, the walls of an ink flow path are formed by patterning using a photosensitive negative resist, and then, a plate having ink discharge ports formed by electro-casting or excimer laser processing is bonded to the element base plate; and
A method of manufacture in which the element base plate manufactured by the same method as described above is prepared, and an ink flow path and ink discharge ports are processed on a resin film (usually, polyimide is preferably used) having a bonding layer thereon by means of excimer laser, and then, the liquid flow-path structural plate thus processed and the aforesaid element base plate are adhesively bonded by applying heat under pressure.
For the ink jet head thus manufactured, it is necessary to make the distance between each heater and discharge port, which exerts influence on the discharge amount, as small as possible in order to discharge micro liquid droplets for high-quality recording. To this end, it is also necessary to lower the height of ink flow path, as well as to downsize the discharge chamber serving as the bubble generating chamber, which is a part of the ink flow path adjacent to the liquid discharge energy generating portion, and each of the discharge ports. In other words, to enable the head thus manufactured to discharge micro liquid droplets, there is a need for the application of thin film process to the formation of the liquid flow-path structure, which should be laminated on the base plate. However, it is extremely difficult to process thin film liquid flow-path structural plate in high precision and bond it to the base plate.
In order to solve the problems related to these methods of manufacture, a method for manufacturing an ink jet head has been disclosed in the specification of Japanese Patent Publication No. 6-45242, in which on the base plate the liquid discharge energy generating element is formed, a model of ink flow path is patterned using photosensitive material, and a covering resin layer is formed on the aforesaid base plate by coating to cover the model pattern, and then, the photosensitive material used for the model is removed after the formation of an ink discharge port on the covering resin layer, which is communicated with the model of the aforesaid ink flow path (hereinafter, this may be abbreviated as the “injection molding method”). For this method of head manufacture, positive model resist is used as the photosensitive material from the viewpoint of easier removal. In accordance with this method of manufacture, micro processing is possible for the formation of the ink flow path, discharge port, and others in extremely high precision, because semiconductor photolithographic technique is adopted. However, the method of manufacture that adopts such semiconductor method of manufacture fundamentally limits the configuration changes near the ink flow path and discharge port to those in a two-dimensional direction, which is parallel to the element base plate inevitably. In other words, it is impossible to arrange the photosensitive material layer to be multiple layers, because photosensitive material is used for the models of the ink flow path and the discharge port. As a result, the desired pattern, which may provide variations in the height direction, cannot be obtained for the model of the ink flow path or the like. (The configuration in the height direction from the element base plate is limited uniformly.) This inevitably presents an impediment to designing the ink flow path for the implementation of high-speed and stable discharge.
On the other hand, in the specification of Japanese Patent Laid-Open Application 10-291317, there is a disclosure that when processing a liquid flow-path structure by means of excimer laser, the processing depth of resin film is controlled by partially changing the degree of opaqueness of the laser mask so as to implement the configuration changes of the ink flow path in a three-dimensional direction, that is, the direction within the plane parallel to the element base plate, as well as in the height direction from the element base plate. The control of a laser processing of the kind in the depth direction is possible in principle, but the excimer laser, which is used for these kinds of processing, is laser having wide-band high brightness, unlike the one used for exposure of semiconductor, making it extremely difficult to implement the stabilization of laser illumination by suppressing the fluctuation of illuminating intensity within the laser illuminated surface. Particularly, for the ink jet head used for recording high-quality image, unevenness of discharge characteristics, which is thus brought about by the finish variation of the processed shapes of discharge nozzles among themselves, is recognized as unevenness of recorded image. Therefore, the enhancement of processing precision has been an important object to be materialized.
Further, taper given to the laser processed surface may often result in the incapability of forming a micro pattern.